The present invention relates in general to a method of and an apparatus for erasing a magnetic disk. More particularly, the present invention relates to a method of and a device for erasing a recording track formed on the magnetic disk.
Signals representing data are generally recorded on magnetic recording media such as magnetic disks, magnetic tapes, or the like by residual magnetism. The data on disks is written by a read/write head located in a disk drive that writes the data in concentric circles on the disk called tracks. Disk drives with removable media preferably have the capability to read and write disks from earlier generation drives (i.e., older disks). These older disks typically have a lower capacity, and therefore have wider data tracks than the newer disks. For example, a 1.44 megabyte 3.5xe2x80x3 floppy disk drive preferably has the capability to read and write older 750 kilobyte disks, which have substantially wider data tracks. In the older disk drives, wider read/write heads are used to read and write data to the tracks. As technology has improved and the density of data on disks has increased, read/write heads have become narrower. To be able to produce newer generation disk drives economically, the same read/write head is used to read and write both current (narrow track) and older generation (wide track) disks. Because the head""s recording width matches the narrower track width of newer drives, special techniques must be used to correctly write a track on the wider tracks found in older generation disks.
FIG. 1 is a top view diagram of a wider track (from an older generation disk) that has been overwritten with a narrow head (in a later generation disk drive having a narrow head). Old data 110 along the edges of the track 101 remain after the new data 105 has been written. The narrow head writes new data on a track width WN. The wider head reads and writes data on a track width WW. The old data remaining after the narrow head writes on a track has a width of WO1 and WO2, where WW=WN+WO1+WO2. Typically, WO1 is substantially equal to WO2. The old data 110 will likely interfere with the desired signal (which comprises only the new data 105 and not the old data 110) if the disk is read in an older drive that is equipped with a wider read/write head. When the track 101 written by a narrow head is read back by a wide head (e.g., in an older drive), both the old data 110 remaining along the track edges and the new data 105 are read back.
One method of overcoming this problem is to utilize a second erase head in the newer drive. This head is not designed to record data, but instead is designed to simply erase the track edges of the older disk""s track. In other words, the recorded signals or data can be erased by removing the residual magnetism under a magnetic field generated by an erasing head positioned closely to the magnetic recording medium. One conventional way for erasing the recorded magnetic signals is known as a DC (direct current) erase process which utilizes either an erasing head with a direct current flowing through its coil or an erasing head having a permanent magnet. Such an erasing head produces a magnetic field in a prescribed direction to magnetize the magnetic recording medium uniformly until it is magnetically saturated. The DC erasing head is however disadvantageous in that it leaves noises of high level on the magnetic recording tape when erasing the recorded signals therefrom, thus increasing the distortion rate of signal waveforms which will be recorded and reproduced.
Another method that does not use a separate erase head is to first erase the entire wide track of the older generation disk before writing the data. This technique, called xe2x80x9cthree-pass writexe2x80x9d is performed in accordance with the top view diagrams shown in FIGS. 2A-2C. Here, the track 101 is first erased by doing two erase passes on the wide track with the narrower read/write head 120. On the first pass, as shown in FIG. 2A, old data 110 on one track edge 125 is erased by passing a DC erase current through the read/write head 120 while the head passes along track edge. On the second pass, as shown in FIG. 2B, the remaining edge 130 is erased. Finally, as shown in FIG. 2C, the new data signal 135 is written down the center of the wider track 101 by the narrower head 120. Thus, the new data 135 is not corrupted by the old data 110 when the track is read by a wider read/write head, for example, in an older generation disk drive.
One drawback of the above described downward compatibility techniques is that the actual signal written is narrower than what the earlier generation head writes. This causes the readback signal read by the wider head to be lower. Additionally, because DC erased media still generates some noise in a readback head, the erased track edges still contribute noise to the readback signal. The result is poor signal-to-noise ratio when an older generation drive reads a disk written by a newer generation drive.
Additionally, it has been found that the DC-magnetized edges of a wide track that has been DC erased and then written with a narrow head adversely affects the edges of the written flux changes by coupling flux to the edges of the written signal that have opposite polarity to the DC field. When read by a wide head, this coupling causes an undesirable effect known as pulse-pairing, where readback pulses of one polarity are shifted early in time, and those of the opposite polarity are shifted late. Thus, leaving DC erase fields on track edges when the track is written by a narrow head degrades both signal linearity and signal-to-noise ratio.
In both audio magnetic recording and in data recording, it is known that erasing the recording medium with a high-frequency AC (alternating current) signal instead of a DC erase field results in lower readback noise. This is because DC erased media is still strongly magnetized in one direction, and any flaws in the media""s distribution of magnetic particles (caused by media defects, random magnetic particle fluctuations, particle clumping, and surface roughness) will result in an external magnetic field that is picked up by the system readback head as unwanted noise.
In a prior art AC erase technique, an erasing head having a coil is supplied with an alternating current for magnetizing the magnetic recording medium as it passes the erasing head. The magnetic recording media is magnetized until it is saturated. As the magnetic recording medium travels away from the AC erasing head, the recording medium is less subject to the alternating magnetic field produced by the AC erasing head, and hence the residual magnetism on the recording medium is progressively reduced, and any residual that remains on the disk is at a frequency above the recording bandwidth, which can be removed by appropriate low-pass filtering.
Thus, the DC magnetized media causes external fields in any anomalous regions including bit edges. By erasing with an AC signal whose frequency is substantially higher than any recorded data frequency, the media magnetization switches polarity over short readback spacings, and the perturbations mentioned above cause lower external fields. Because polarity shifts frequently with AC erase, externally generated fields are smaller. This results in lower unwanted readback noise. However, conventional AC erase systems are single pass.
Although the art of reading and writing data to disks is well developed, there remain some problems inherent in this technology, particularly the integrity of data written to and read from different generations of disks and disk drives having different size read/write heads. Therefore, a need exists for a system and method for erasing unwanted data that overcomes the drawbacks of the prior art.
The present invention is directed to a system for erasing a signal in a recording track formed on a magnetic disk comprising a magnetic head for at least erasing a first edge portion and a second edge portion of the magnetic disk, and an AC erase controller for sequentially generating a first AC erasing signal and a second AC erasing signal. The AC erase controller comprises a terminal for receiving an erase command signal, and the AC erase controller supplies the magnetic head with the erasing signals responsive to the erase command signal. The first AC erasing signal is for erasing the first edge portion and the second AC erasing signal is for erasing the second edge portion of the magnetic disk.
According to one aspect of the present invention, the first edge portion of the magnetic disk is opposite the second edge portion of the magnetic disk.
In accordance with an aspect of the present invention, the AC erase controller comprises a gate oscillator. Preferably, the gate oscillator comprises XOR gates.
In accordance with a further aspect of the present invention, the system further comprises a pulse detector for detecting the erase command signal and activating the AC erase controller responsive to the erase command signal.
In accordance with a further aspect of the present invention, the erase command signal is a DC erase command signal or an AC erase command signal.
According to further aspects of the invention, the first AC erasing signal has a first frequency and the second AC erasing signal has a second frequency. The first and second frequency are substantially equal, and preferably equal about 50 MHz.
In a further embodiment within the scope of the present invention, a method for erasing a signal in a recording track formed on a magnetic disk is provided. The method comprises the steps of erasing a first portion of the recording track by supplying through a magnetic head a first AC erasing signal, and erasing a second portion of the recording track by supplying through the magnetic head a second AC erasing signal. The first portion of the recording track is along one edge of the recording track and the second portion of the recording track is along the opposite edge of the recording track.
Another embodiment within the scope of this invention includes a method for erasing a signal in a recording track formed on a magnetic disk, comprising the steps of receiving an erase command signal at an AC erase controller, supplying a magnetic head with a first AC erasing signal responsive to the erase command signal, and supplying the magnetic head with a second AC erasing signal responsive to the erase command signal.
According to another aspect of the present invention, the method further comprises the steps of erasing a first portion of the recording track by supplying through the magnetic head the first AC erasing signal, and erasing a second portion of the recording track by supplying through the magnetic head the second AC erasing signal.
The foregoing and other aspects of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.